This application is based on and incorporates herein by reference Japanese Patent Application Nos. Hei. 11-346386 filed on Dec. 6, 1999, and Hei. 11-365827 filed on Dec. 24, 1999.
1. Field of the Invention
The present invention relates to an internal combustion engine exhaust gas purification apparatus for purifying exhaust gas from the internal combustion engine by removing HC from the exhaust gas.
2. Description of Related Art
An ordinary gasoline engine made in recent years has a three-way catalyst provided in an exhaust pipe thereof for purifying exhaust gas by removing noxious components of the exhaust gas such as HG, GO (carbon monoxide) and NOx (nitrogen oxide) from the gas. In the cold state of the internal combustion engine right after an engine start, however, the temperature of the three-way catalyst does not rise to an activation temperature. That is, the three-way catalyst is still in a non-activated state right after the engine start. Thus, the three-way catalyst is not capable of purifying the exhaust gas sufficiently. As a result, the exhaust emission is worsened.
In order to solve this problem, an HC absorbing catalyst is installed at the downstream side of a three-way catalyst as is disclosed in JP-A-11-82111. The HC absorbing catalyst absorbs HC having passed through the three-way catalyst, which is still in a non-activated state. The disclosed HC absorbing catalyst is a two-layer coat catalyst, which is made by coating the surface of the HC absorbing layer for absorbing HC with a layer of a three-way catalyst. When the layer of the three-way catalyst of the two-layer coat catalyst is put in an activated state, the layer of the three-way catalyst removes HC released from the HC absorbing layer.
In the cold state of the internal combustion engine right after the engine start, the state of fuel combustion is unstable, generating a considerably large amount of unburned HC. Thus, when it takes a long time to activate the three-way catalyst or the two-layer coat catalyst, the amount of HC absorbed by the two-layer coat catalyst becomes saturated, thereby making it no longer possible for the catalyst to absorb HC. As a result, the amount of HC exhausted to the atmosphere increases. In order to solve this problem, the size of two-layer coat catalyst is increased. However, not only does this solution dissatisfy a demand for a low cost and space saving, but it also takes an even longer time to raise the temperature of the two-layer coat catalyst or to activate the two-layer coat catalyst.
In particular, in a configuration wherein the two-layer coat catalyst is installed at the downstream side of the three-way catalyst as in the disclosed case, since the distance from the engine to the two-layer coat catalyst is large, the gas loses heat before the time when the exhaust gas enters into the catalyst, thereby inevitably decreasing the temperature thereof. Thus, it unavoidably takes too long time to increase the temperature of the two-layer coat catalyst or to activate the catalyst. In the mean time, the amount of HC absorbed by the HC absorbing layer becomes saturated. As a result, the HC absorbing layer is no longer capable of absorbing HC.
Further, in order to solve the above described problem, there has been adopted a technique to heat a catalyst to an activation temperature at an early time by raising the exhaust gas temperature through execution of control to heat the catalyst early such as ignition retard control at an engine cold start. In order to further improve a catalyst-warming function, as is disclosed in JP-A-9-96216, there has been proposed a technique whereby, during execution of control to heat a catalyst at an early time, injection of fuel into some cylinders of the engine is halted in order to increase the concentration of oxygen (the amount of unburned air) in the exhaust gas, and the amount of fuel injected into the remaining working cylinders is raised in order to increase the quantities of rich components of the exhaust gas such as HC and CO so as to drive an ignition device such as a glow plug provided in an exhaust pipe to ignite the exhaust gas to generate after-burning in the exhaust pipe, and to use heat generated by the after-burning for warming the catalyst. Here, a cylinder, injection of fuel to which is halted, is referred to as a halted-injection cylinder.
However, in JP-A-9-96216, in order to generate the after-burning in the exhaust pipe, it is necessary to install an ignition device such as a glow plug in the exhaust pipe. Thus, the proposed technique has problems of complicated configuration and high cost.
An object of the present invention addressing such problems to provide an exhaust gas purification apparatus of an internal combustion engine capable of substantially reducing the amount of HC exhausted at an engine start.
In order to achieve the object, in order to remove HC (HC) released from a HC absorbent within a catalyst for absorbing HC due to a rising temperature of the substance, an exhaust gas purification apparatus according to a first aspect of the present invention is provided with a catalyst-early-warming means for early raising the temperature of the catalyst right after the internal combustion engine start to activate the catalyst at an early time. Since the catalyst can be activated with certainty right after the internal combustion engine start before the amount of HC absorbed by the HC absorbent reaches a saturation level, the HC absorbent is capable of absorbing unburned HC reliably right after the engine start, thereby allowing the exhaust gas to be cleaned by the catalyst. Therefore, the amount of HC exhausted right after the engine start can be considerably reduced in comparison with the conventional catalyst. In addition, the time for activation of the catalyst can be made shorter. Thus, the amount of HC absorbed by the HC absorbent can be reduced by a quantity proportional the decrease in time. As a result, it is possible to satisfy the demand for a low cost and space saving without the need to increase the size of the HC absorbent.
In this case, the farther the exhaust gas flows in the downstream direction of the exhaust-gas path, the more the temperature of the exhaust gas decreases. Thus, when the catalyst for removing HG released from the HG absorbent is provided at the downstream side of the HG absorbent, the HG absorbent will be heated to a releasing temperature before the catalyst reaches an activation temperature. As a result, it is feared that HG released from the HG absorbent cannot be removed by using the catalyst and is exhausted to the atmosphere. In addition, there also exists the fact that the releasing temperature of the HG absorbent is generally lower than the activation temperature of the catalyst.
Taking the above absorption rates into consideration, the catalyst for removing HC released from the HC absorbent may be provided at the upstream side of the HC absorbent, and the HC released from the HC absorbent may be returned to the upstream side of the catalyst through a reflux path. As an alternative, the catalyst is held on the surface of the HC absorbent to form an integrated two-layer coat catalyst including the catalyst and the HC absorbent, and the two-layer coat catalyst is provided at a location in close to an exhaust manifold as in the case with an exhaust gas purification apparatus.
By employing the two-layer coat catalyst, the catalyst in the upper layer directly exposed to exhaust gas is heated first to an activation temperature before the HC absorbent in the lower layer is heated to an releasing temperature so that the catalyst in the upper layer is capable of removing HC released from the HC absorbent with certainty. In addition, by providing the two-layer coat catalyst at a location in close to the exhaust manifold, the catalyst can be exposed to high temperature exhaust gas. Thus, the catalyst can be activated in an even shorter period of time by the high-temperature exhaust gas in conjunction with a catalyst early-warming effect provided by the catalyst-early-warming means. As a result, the effect of reducing the amount of HC exhausted at the internal combustion engine start can be further increased.
A second object of the present invention is to provide an early-warming control apparatus that is capable of warming a catalyst for purifying exhaust gas at an early time by generating after-burning inside a path through which the exhaust gas flows without an ignition device in the path, and offers a simplified configuration and a reduced cost as well as an improved catalyst-warming function.
In order to achieve the object, in an early-warming control apparatus for warming a catalyst for purifying exhaust gas of an internal combustion engine at an early time in accordance with a second aspect of the present invention, in execution of control to heat a catalyst at an early time, an exhaust-gas-heating control means executes ignition retard control to raise the exhaust gas temperature making a rich component of the exhaust gas burnable inside the path, and a cylinder deactivation operation control means halts injection of fuel into some cylinders of the internal combustion engine, operating the internal combustion engine by using the remaining cylinders. A cylinder, injection of fuel to which is halted, is referred to as a halted-injection cylinder and the remaining cylinders are each known as a working cylinder. By doing so, in execution of the control to heat a catalyst at an early time, gas exhausted by the working cylinder is heated to the temperature making the exhausted gas burnable inside the path due to the ignition retard control. Thus, when rich components such as HG and CO of this high-temperature exhaust gas are mixed with oxygen of unburned air exhausted by the halted-injection cylinder, after-burning occurs in the path and the temperature of the catalyst is raised by combustion heat generated by the after-burning. As a result, the catalyst can be heated at an early time after the engine start and, since there is no need to install an ignition device for igniting exhaust gas, the configuration can be made simple and the cost can be reduced.